Conductive adhesive compositions comprising an adhesive resin and conductive fillers are used in the fabrication and assembly of semiconductor packages and microelectronic devices, both to mechanically attach, and to create electrical and thermal conductivity between, integrated circuit devices and their substrates. The most commonly used conductive filler is silver flake. Adhesive resins are used in the conductive compositions because silver flake typically do not sufficiently adhere semiconductor or microelectronic devices to their substrate. The presence of the resin, however, limits the high thermal and electrical conductance of the silver.
Currently, conductive compositions containing only silver and no resin are being adhered with thermo-compression bonding, or no pressure bonding, to silver or gold substrates. However, substrates commonly used in the fabrication of electronic devices are copper lead-frames, and silver does not readily form an inter-metallic bond to copper. Solders have been used, but in high power and high temperature applications, solder fails when cycled at high temperatures or temperatures close to its melt temperature. Moreover, solder requires the presence of fluxing agents, which leave flux residues after the inter-metallic bond is formed, thus necessitating a cleaning step for the substrate.
It would be an advantage to have a silver composition containing no adhesive resin that can sinter and adhere to copper, and that can adhere with increased strength to silver and gold substrates than can now be obtained.